Be sure the air that's being drawn OUT the 1 fan is being drawn IN from the outside. In other words, if you only have 1 fan, it will work reeeeeal hard to draw its air from the main house. This will create a minor vacume and certainly send your CAC bill up through the roof (maybe literally.) Remember, air out must = air in. Even when it's 90 degrees outside, you'll want outside air as your source; not house air.
A better scenario for a finished attic is done BEFORE the attic is finished. Usually, soffit vents are installed along with a ridge vent. And in between the roof rafters, we install soffit shutes. This allows outside air to rise up through the soffits, run under the roof's sheathing to cool it, and out the ridge vent. All done by natural convection. Then, you can insulate the roof and install the finished drywall. Who knows what's under your finished roof in the attic. With the aformentioned construction, the attic can be heated and cooled with conventional means. In your scenario, it needs to be treated as a SEPARATE room, as if it's NOT part of the main house. That's why you need a separate 'source' of air, and NOT use the air from the main house.